Three tachykinins, Substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) are widely distributed throughout the peripheral and central nervous systems. The biological effects of these neuropeptides are carried out via binding to their preferred receptors, NK1, NK2 and NK3 (Guard, S. and Watson, S. P. Neurochem. Int. 1991, 18, 149). Substance P displays highest affinity for the NK1 receptors, whereas NKA and NKB bind preferentially to NK2 and NK3 receptors, respectively. The selectivities of the endogenous ligands for their respective receptors are not absolute (reviewed in Regoli, D. et al. Pharmacol. Rev. 1994, 46, No. 4, 551 plus Bremer, A. A. et al. Eur J Pharmacol 2001, 423, 143). The three receptor subtypes belong to the G-protein-coupled receptor super family and have been cloned in various species including mice, rats and humans (Giardina, G. A. M. et al. Drugs of the Future 1997, 22, 1235 and references herein).
Activation of the tachykinin receptors influences a broad array of biological actions, including pain transmission, vasodilation, smooth muscle contraction, secretion of saliva, bronchoconstriction, activation of the immune system (inflammatory pain), neurogenic inflammation and neurotransmission (Patacchini, R. et Maggi, C. A. Eur J Pharmacol. 2001, 429, 13; Longmore, J. et al. Can J Physiol Pharmacol 1997, 75, 612; Giardina, G. A. M. et al. Drugs of the Future 1997, 22, 1235 and references herein).
Expression of NK2 receptors in human is somewhat controversial. The receptor is generally expressed in low amounts in CNS, and autoradiographic studies have failed to show NK2 receptors in the human brain. A recent reverse transcription-polymerase chain reaction (RT-PCR) study, however, has revealed a detectable expression of NK2 receptor mRNA in various human brain regions including caudate nucleus, putamen, hippocampus, substantia nigra and cerebral cortex (Bensaid, M et al. Neurosci Lett 2001, 303, 25).
Up-regulation of the preprotachykinin (PPT) genes and mRNAs for the neurokinin receptors occurs both in animal models of disease (Fischer, A. et al. J Clin Invest 1996, 98, 2284) and in human diseases, such as asthma (Adcock, I. M. et al. J Mol Endocrino 1993, 11, 1).
NK antagonists have been and are under investigations for the treatment of a vast amount of both CNS related and peripheral diseases. A number of pre-clinical studies have been performed to assess the involvement of NK1 and NK2 receptors mediation and modulation of diseases related to anxiety and/or depression (Griebel, G. Et al. Psychopharmacology, 2001, 158, 241; Walsh, D. M. et al. Psychopharmacology 1995, 121, 186; Rupniak, N. M. et al. Neuropharmacology 2000, 39, 1413; Rupniak, N. M. et Kramer, M. S. TiPS 1999, 20, 485; ; Giardina, G. A. M. et al. Drugs of the Future 1997, 22, 1235, and references in these).
These studies indicate that NK2 antagonists will be useful in treating or preventing a variety of brain disorders including depression, manic depression, bipolar disorder, dysthymia, mixed anxiety depression, generalised anxiety disorder, social anxiety disorder, panic anxiety disorder, post traumatic stress disorder, obsessive compulsive disorder, acute stress disorder, phobia, pre-menstrual dysphoric disorder, psychosis, and Huntington's disease as well as Parkinson's disease, adjustment disorders, pain, emesis, migraine, epilepsia, obesity, asthma and cerebrovascular disease. However, peripheral diseases such as inflammation, inflammatory bowel disease, hypertension, arthritis, cardiovascular diseases, neuritis, neuralgia, urticaria, incontinence, gastrointestinal diseases, influenza, allergy, pulmonary allergy and carcinoma/tumoral growth may also be addressed by NK2 antagonists.
U.S. Pat. No. 3,994,891 discloses tetrahydroisoquinolines of the general formula
wherein R is hydrogen or methyl, and G is NH or CH2. The dihydroxy compounds are described as effective vasodilators, whereas the dimethoxy compounds are intermediates in the manufacture of the dihydroxy compounds.
Hence, there is a desire for novel compounds that are antagonists at the NK2 receptor.